1. Field of the Invention
The invention relates to semiconductor manufacturing. More particularly, the invention relates to an improved wire bonding capillary used in the bonding of wires to the bond pads of a semiconductor device and the leads of a lead frame.
2. Background of the Invention
In semiconductor device manufacturing, a wire bonding process is used to electrically connect the metal bond pads on the active surface of a semiconductor die to the leads or lead fingers of a lead frame. Wire bonding devices are well known in the art. U.S. Pat. Nos. 3,894,671, 4,877,173, and 5,082,154 illustrate wire bonding devices.
The wire bonding process occurs during the final stages of manufacture of the semiconductor device before the semiconductor device is enclosed within a sealed or encapsulated package. Although a variety of different packaging systems are used, most packaging systems include a lead frame on which the semiconductor die is mounted. The lead frame has lead fingers which are connected to the bond pads on the active surface of the semiconductor die through the use of wires bonded to the lead fingers and bond pads. Subsequently, the semiconductor die, wires, and portions of the lead fingers and lead frame are encapsulated in plastic during a molding process. After the molding process, the portions of the lead fingers extending beyond the molded plastic material are trimmed and formed into the desired configuration for the use and mounting of the semiconductor device on a substrate.
The wires used to connect the bond pads of the semiconductor die to the lead fingers of the lead frame are small in diameter, have as short a length as possible, and are typically of gold. During the wire bonding process, a heat block heats the semiconductor die and the lead frame to a temperature in the range of 150.degree. C. to 350.degree. C. A bonding capillary tool mechanically presses the wire against a bond pad on the active surface of the semiconductor die and then to a bonding site on the desired lead finger of the lead frame. The bond wire is threaded through the bonding capillary for use in the bonding process. The end of the wire threaded through the bonding capillary is then heated by an electrical discharge or a hydrogen torch to a molten state, thereby forming a ball of molten material on the end of the bond wire extending from the bonding capillary. The molten ball is pressed by the bonding capillary against the heated bond pad on the active surface of the semiconductor die to alloy the metallic elements of the wire and the bond pad, thereby bonding the wire to the bond pad in a ball type wire bond. In some instances, ultrasonic vibration of the bonding capillary may be used during the bonding process. After the bonding of the wire to the bond pad on the active surface of a semiconductor die, the bonding capillary tool is moved to a bonding site on the desired lead finger of the lead frame. The wire is pressed against the heated lead finger of the lead frame to bond the wire to the lead finger. The bond wire is then tensioned by the bonding capillary until the wire is sheared, making a stitch or wedge type wire bond on the lead finger. The bonding process is repeated for the desired bond pads on the active surface of the semiconductor die for connections to the desired lead fingers of the lead frame.
One type of wire bonding capillary design is illustrated in U.S. Pat. No. 4,415,115. The bonding capillary tip is formed having a flat bonding surface and an annular cutting ridge raised from the flat bond surface surrounding the aperture through which the wire is fed in the bonding capillary. Alternately, the cutting ridge may comprise a semicircle shape rather than an annular shape.
Another type of wire bonding capillary is illustrated in U.S. Pat. No. 5,421,503. The bonding capillary is for use in automatic gold ball bonders for bonding fine gold wires onto closely spaced bond pads on semiconductor devices. The bonding capillary comprises a cylindrical body portion which fits into an ultrasonic transducer having a bottle-neck working tip on the other end of the body portion. The working tip includes a working face comprising an annular ring between the chamfer diameter of the working tip and the working tip diameter and a face angle of approximately 22 degrees plus or minus 3 degrees.
Yet another wire bonding capillary is illustrated in U.S. Pat. No. 5,662,261. The wire bonding capillary includes a working tip having an elongated hole therethrough and a face extending away from the hole at multiple angles of increasing magnitude.
While the size of semiconductor devices continues to decrease and the number of bond pads on the active surface continues to increase, having smaller pitch between adjacent bond pads and the width of lead fingers of lead frames decreases, it is necessary to have a wire bonding capillary which will form effective ball type wire bonds on the bond pads of the semiconductor device and stitch or wedge type wire bonds on the lead fingers of the lead frame having acceptable pull-off strength characteristics without damaging the circuitry of the semiconductor device. Such requirements illustrate the need for a wire bonding capillary which will effectively make a ball type wire bond on the bond pad of the semiconductor device without contacting the surface of the semiconductor device adjacent thereto and will effectively make stitch or wedge type wire bonds on the lead fingers of lead frames.